The key points to identify;
a) The TSA does not make flying safe. The FAA makes flying safe. The TSA allegedly keeps bombs off planes but going by their press releases they've never actually done this. It's always some kid with a pen-knife.
b) For years Customs have been attempting the opposite goal, detecting stuff coming off planes. They have a good success rate, but clearly plenty of stuff gets through. Is there any evidence that the TSA has a better success rate?
c) It's not hard to get forbidden items onto a plane. It just isn't. All the TSA does is make it harder to do it via the main entrance hall. Given the amount of merchandise, and number of people who work on the "other side" of the security barrier, does anyone think it's hard? For example it's easy to take liquids on a plane, just buy them in the departure hall. [edit - It's also not hard to get a job as a TSA agent. Quis custodiet ipsos custodes?]
d) Given that the TSA doesn't make us any _safer_, it's hard to find a reason for it to exist. But large govt. departments do not go softly into the night.
It takes sustained, broad-based pressure to make this sufficiently important for politicians to get involved. Until that happens _nothing_ will change. No, I lie, until that happens the TSA will spend more money, and intrude on our lives more, but won't actually provide any benefit.